Java EE Pattern: Infrastructure

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1
Session:
Pattern of the Infrastructure Layer
Bean Locator
Payload Extractor
Asynchronous Resource Integrator
Resource Binder

2
Objectives
Learn about:
✔ How to access other components using JNDI instead of CDI
✔ How enhance robustness in the field of messaging and message
types
✔ How to integrate 3rd party systems using Messaging
✔ An alternative to @Inject

3
Some orientation
Consumer
Consumer
Layer
Integration
Layer
Business Process
Layer
Services
Layer
Component
Layer
OS
Layer

4
ECB Pattern
Entity Control Boundary
✔ Based upon Robustness Diagrams
(http://www.agilemodeling.com/artifacts/robustnessDiagram.htm)
➢ Boundary: user interface
➢ Control: actual process or activity
➢ Entity: a concept from an enterprise context.
✔ Elements are generic enough to be mapped either to service-
oriented or object-oriented architectures.
Boundary Control Entity
Adam Bien

5
Services, components and patterns
DAO &
Domain
Store
Generic
DAO
Singleton
Service
Starter
Dual View
SOA Facade
Lightweight
asynchronous
Facade
Multichannel
Facade
TO
&
DTO
Paginator
Bean
Locator
Multichannel
Facade
Resource
Binder
Payload
Extractor
Aynchronous
Resource
Integrator
Infrastructure

6
Module
Bean Locator

7
Bean Locator
According to Adam Bien, Dependency Injection
has also some disadvantages:
➢ It is static - the dependencies are resolved at start
time.
➢ The service user has to live with the given contracts
or conventions.
➢ DI is only available for certain classes which are managed by a
container.
✔ Sometimes the need to rely on JNDI lookups might occur.
✔ A convenient way to access these ressouces should be provided

8
You have to decide
✔ .. whether EJBs from different jars should be injected (ear
deployment only) or looked-up for.

9
JNDI names
✔ Have not been standardized for a long time
✔ EJB 3.1 solves the above problem by mandating that every
container must assign (at least one) well defined global JNDI
names to EJBs.
✔ The general syntax of a (portable) global JNDI name of an EJB is of
the form:
✔ BUT: application name and module name vary if using maven
Right now I'm working with 3 different ejb containers (Glassfish, JBoss and
OpenEjb) and they use totally different conventions for ejb names. It's
incredible, isn't it?
--- Posted by Filippo on December 24, 2006 at 09:25 AM CET
java:global/[<application-name>]/<module-name>/<bean-name>!
<fully-qualified-bean-interface-name>

10
Even within ...
✔ … the same JBoss 6.1 but different configurations, lookup will be
different:
default configuration
standard configuration

11
Service Locator 2.0 (Bean Locator)
✔ We need to find something which is configurable and allows to
retrieve the JNDI name at runtime:
➢ Combination of Builder pattern and Strategy pattern
➢ Builder pattern: construct the utility class
➢ Strategy pattern: various strategies to create
the appropriate JNDI look-up string

12
Implementation

13
Lab
Implement Bean Locator
(not more than 15 min.)

14
Module
Resource Binder

15
Resource Binder
✔ Application server registeres resources like EJBs, JMS destinations
or DataSources at startup time
✔ These components are injectable into Servlets and/or EJBs
✔ If you want to do the same with your components, you need to do
a little work:
➢ Make use of the @Inject annotation and a DI framework like WELD or
Google Guice
➢ Bind the resources yourself into JNDI and inject later on using
@Resource annotation

16
Injecting by @Inject
✔ The @Inject annotation provides a convenient way to inject non-
EJB resources
✔ @Inject is more general than EJB and is part of CDI specification.
So if you want to use @Inject, you need an implementation of it in
your server.
✔ For POJOs (not EJBs) you have to
use @Inject.
✔ In JBoss/WELD using @Inject
requires the jar to contain a
beans.xml file in
META-INF subdirectory

17
Using @Inject
Example:
@Stateless
@Remote(SomeService.class)
public class SomeServiceBean implements SomeService
{
@Inject
private SomeProcess process;
public void someBusinessMethod(int amount) throws ProcessException
{
// was before
//de.brockhaus.userMgmt.util.Process p =
new de.brockhaus.userMgmt.control.process.SomeProcess(amount);
process.setAmount(amount);
process.proceed();
}
}

18
Using @Resource
✔ Alternatively the @Resource annotation can be used to access
resources bound to the JNDI tree
✔ As the result is the same compared to @Inject, @Inject is less
work …
✔ The @Resource annotation explained for being complete only
✔ Doesn't work under JBoss 6.1 if resource is bound by Singleton
bean with @PostConstruct and
@DependsOn annotations

19
Binding the resources
@Singleton
@Startup
public class ResourceBinder
{
private Logger log = Logger.getLogger(this.getClass());
@PostConstruct
public void bindResources()
{
try
{
InitialContext ctx = new InitialContext();
ctx.rebind("SomeProcess", new SomeProcess());
log.info(">>>>> SomeProcess bound");
}
catch (NamingException e)
{
e.printStackTrace();
}
}
}

20
Injecting the resource
✔ Using @Resource annotation
@Stateless
@Remote(SomeService.class)
public class SomeServiceBean implements SomeService
{
@Resource(mappedName="SomeProcess")
private SomeProcess process;
public void someBusinessMethod(int amount) throws ProcessException
{
process.setAmount(amount);
process.proceed();
}
}

21
Lab
Implement Resource Binder

22
Module
Payload Extractor

23
Extracting the payload
Why:
✔ As no one Type checking and error handling needs to be factored
out from the MDB
✔ Corrupted messages have to be send to DLQ
Approach:
✔ Decorate onMessage() method of
MDB using an interceptor

24
The interceptor
✔ ...
public class PayloadInterceptor
{
private static final String CALLED_METHOD_NAME = "proceedXMLMessage";
@AroundInvoke
public Object intercept(InvocationContext ctx){
Object ret = null;
try{
// getting the parameters from InvocationContext
Object[] params = ctx.getParameters();
if(params[0] instanceof TextMessage){
TextMessage msg = (TextMessage) params[0];
String payload = msg.getText();
this.invokeMethod(ctx.getTarget(), payload);
log.info("TextMessage received");
}
ret = ctx.proceed();
}
catch (Exception e){
this.dealWithException(e);
}
return ret;
}

25
Wrapping the MDB
✔ onMessage method annotated, service injected ...
@MessageDriven(
activationConfig = {
@ActivationConfigProperty(propertyName = "acknowledgeMode",
propertyValue = "Auto-acknowledge"),
@ActivationConfigProperty(propertyName = "destinationType",
propertyValue = "javax.jms.Queue"),
@ActivationConfigProperty(propertyName="destination",
propertyValue="queue/facade/UserMgmt")
})
public class UserManagementQueueListenerBean implements MessageListener {
@EJB
private UserManagementServiceLocal userService;
@Interceptors(PayloadInterceptor.class)
public void onMessage(Message msg){
log.info("invoked but nothing will happen");
}
...

26
Wrapping the MDB
✔ Delegating to the service ...
public void proceedXMLMessage(String xml) throws JAXBException
{
log.info(xml + "received");
userService.createUserThroughXML(xml);
}

27
Lab
Implement Payload Extractor

28
Module
Asynchronous Resource
Integrator

29
Purpose
✔ In the majority of the environments, many applications still run on
heterogeneous platforms (heterogeneosity meant in terms of
technologies like programming languages)
✔ Existing Java EE services need to be integrated with these legacy
services.
✔ There are several technologies you might
want to make use of like HTTP-based
REST or SOAP or even CORBA.
✔ If Messaging is supported on both
platforms, why not using it?

30
Lab
Implement Asynchronous Resource Integrator

31
Review
Session Review:
✔ Why do we need to access other components not using JNDI?
✔ Is there a way to get out of the JNDI name hazzle?
✔ Messaging is nice but which types of messages to deal with and
how to check?

32
Recommeded reading
✔ http://java.sun.com/blueprints/corej2eepatterns/
✔ http://www.corej2eepatterns.com/Patterns2ndEd/
✔ Adam Bien, J2EE Patterns,
Addison Wesley 2002,
ISBN: 3-8273-1903-X
✔ Floyd Marinescu, Ed Roman:
Ejb Design Patterns: Advanced Patterns,
Processes, and Idioms; Wiley & Sons,
ISBN-10: 0471208310
✔ And other ...
Photo: Bundesarchiv

Java EE Pattern: Infrastructure

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